In order to investigate total organic carbon TOC exchange through the Strait of Gibraltar, samples were taken along two Ž. Ž. sections from the western Gulf of Cadiz and eastern Western Alboran Sea entrances of the Strait and at the middle of thé Strait in April 1998. TOC was measured by using a high-temperature catalytic oxidation method. The results referenced here are based on a three-layer model of water mass exchange through the Strait, which includes the Atlantic inflow, Mediterranean outflow and an interface layer in between. All layers were characterised by a decrease of TOC concentrations from the Gulf of Cadiz to the Western Alboran Sea: from 60-79 to 59-66 mM C in the Atlantic inflow and from 40-60 tó 38-52 mM C in the Mediterranean waters, respectively. TOC concentrations in the modified North Atlantic Central Water Ž. varied from 43 to 55 mM C. Intermediate TOC values were measured in the interface layer 43-60 mM C. TOC concentrations increased from the middle of the Strait towards continents indicating a contribution of organic carbon of photosynthetic origin along Spain and Morocco coasts or TOC accumulation due to upwelling in the northeastern part of the Strait. Our results indicate that the short-term variability caused by the tide greatly impacts the TOC distribution, particularly in the Gulf of Cadiz. The TOC input from the Atlantic Ocean to the Mediterranean Sea through the Strait of Gibraltar varieś 4 4 y 1 Ž 12 12 y 1. from 0.9 = 10 to 1.0 = 10 mol C s or 0.28 = 10 to 0.35 = 10 mol C year , respectively. This estimate suggests that the TOC inflow and outflow through the Strait of Gibraltar are two and three orders of magnitude higher than reported via the Turkish Straits and Mediterranean River inputs.

The total organic carbon (TOC) and total inorganic carbon (C 2) exchange between the Atlantic Ocean and the Mediterranean Sea was studied in the Strait of Gibraltar in September 1997. Samples were taken at eight stations from western and eastern entrances of the Strait and at the middle of the Strait (Tarifa Narrows). TOC was analyzed by a high-temperature catalytic oxidation method, and C 2 was calculated from alkalinity}pH 2 pairs and appropriate thermodynamic relationships. The results are used in a two-layer model of water mass exchange through the Strait, which includes the Atlantic in#ow, the Mediterranean out#ow and the interface layer in between. Our observations show a decrease of TOC and an increase of C 2 concentrations from the surface to the bottom: 71}132 M C and 2068}2150 mol kg\ in the Surface Atlantic Water, 74 }95 M C and 2119}214 8 mol kg\ in the North Atlantic Central Water, 63}116 M C and 2123}2312 mol kg\ in the interface layer, and 61}78 M C and 2307}2325 mol kg\ in the Mediterranean waters. However, within the Mediterranean out#ow, we found that the concentrations of carbon were higher at the western side of the Strait (75}78 M C, 2068}2318 mol kg\) than at the eastern side (61}69 M C, 2082}2324 mol kg\). This di!erence is due to the mixing between the Atlantic in#ow and the Mediterranean out#ow on the west of the Strait, which results in a #ux of organic carbon from the in#ow to the out#ow and an opposite #ux of inorganic carbon. We estimate that the TOC input from the Atlantic Ocean to the Mediterranean Sea through the Strait of Gibraltar varies from (0.97$0.8)10 to (1.81$0.90)10 mol C s\ (0.3;10 to 0.56;10 mol C yr\), while out#ow of inorganic carbon ranges from (12.5$0.4)10 to (15.6$0.4)10 mol C s\ (3.99}4 .90;10 mol C yr\). The high variability of carbon exchange within the Strait is due to the variability of vertical mixing between in#ow and out#ow along the Strait. The prevalence of organic carbon in#ow and inorganic carbon out#ow shows the

[1] In the eastern North Atlantic, carbon dioxide fugacity (fCO 2 ) in the upper mixed layer and discrete pH and total alkalinity measurements in the upper 2000 m were studied during three cruises (winter, spring, and summer 2001) within the framework of the Programme Océan Multidisciplinaire Méso Echelle (POMME) project. This extensive region is located between 39°and 45°N and 16°and 21°W. The mesoscale variability of fCO 2 on the sea surface and in the atmosphere during each season was determined to understand the mechanisms of evolution that control the spatial and temporal variability of fCO 2 together with an estimation of the fluxes of CO 2 between the atmosphere and the ocean. If we consider the observation to be 22 days per cruise, the region was in-taking 0.30 Tg C during the winter cruise and 0.36 Tg C during the spring cruise, whereas it was out-gassing 0.07 Tg C during the summer cruise. These values are clear indications that the area is acting as a sink of CO 2 on an annual scale, with an estimated flux value of À1.1 mol m À2 yr À1 , which is over twice as much as the mean global flux of À0.5 mol m À2 yr À1 (Takahashi et al., 2002). The changes with time observed in the fCO 2 values over the surface layer between the winter and the spring cruises have been described considering thermodynamics, gas exchange, water transport, and biological activity in the area. The estimation of the subduction of inorganic carbon yielded a value of 0.25 Pg C yr À1 , which is approximately 10% of the global net oceanic CO 2 sink flux.Citation: González Dávila, M., J. M. Santana-Casiano, L. Merlivat, L. Barbero-Muñoz, and E. V. Dafner (2005), Fluxes of CO 2 between the atmosphere and the ocean during the POMME project in the northeast Atlantic Ocean during 2001,

All existing descriptions of nutrient distributions in the Strait of Gibraltar suggest that the Atlantic water brings to the Mediterranean Sea nutrients in the Redfield ratio (N:Si:P = 16:15:1). Here, the N:Si:P molar ratios (±Standard Error), obtained in April 1998, are used to show that in the Atlantic water at the western entrance of the Strait this ratio is lower (13.8(±0.5):12.1(±1.0):1) than the classical Redfield ratio; it is close to the Redfield ratio in the middle of the Strait (15.6(±0.6):10.7(±0.9):1), and increases dramatically to 23.6(±3.4):29.1(±4.5):1 at the eastern entrance of the Strait. In the Mediterranean water, the N:Si:P ratio has a quite similar trend with 31.5(±6.0):26.5(±3.6):1 in the east, 20.4(±0.2):31.5(±11.1):1 in the middle and 18.1(±0.6):17.6(±0.7):1 in the west of the Strait. The physical and biological processes that account for the observed spatial variability of the N:Si:P ratio along the Strait are identified. We estimated that in the Atlantic water entering the Mediterranean Sea, about 84% of the variability in N:Si:P molar ratio is due to biological and 16% to physical processes.

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Our observations at a traverse of Ca&z in February 1998 indicated dissolved organic carbon (DOC) concentrations ranging from 61 to 89 pM C within the Spanish Shelf Water, from 48 to 64 pM C within the North Atlantic Surface Water, and from 49 to 55 pM C within the North Atlantic Central Water. Moreover, according to temperature and salinity data, the shallow core of the Mediterranean outflow was also identified deeper than 350 m depth with DOC concentrations between 52 and 58 pM C. The data suggest that DOC distribution at the traverse of the Gulf of Cadiz was controlled by outputs of degraded particles transported within alongslope descending shelf waters and also by features of the circulation in the Gulf of Cadiz. An estimate of organic carbon transport suggests that ca 1.34 to 2.68 X 102 m01 C S-' were transported within the shallow core of Mediterranean outflow. This amount of DOC was 2 orders of magnitude less than that calculated within the Mediterranean outflow in the Strait of Gibraltar for the summer and autumn seasons. These processes might partly regulate the biogeochemistry of the shallow core of the Mediterranean outflow along the Iberian coast.

The necessity for determining the role of dissolved organic carbon (DOC) in the global carbon cycle stimulated the development of different methods of DOC analysis in aquatic environments. Progress in this direction has been made by oceanographers who developed and introduced a high-temperature catalytic oxidation (HTC) method for low organic carbon concentrations. Today this method is the reference method for marine DOC study. The combination of available reference materials and the participation in intercalibration exercises has resulted in both an increased accuracy and higher precision for this method. The HTC method completely oxidizes the more resistant DOC; makes information rapidly available following the completion of the field analysis; provides a high precision (down to 0.5 microM C); covers the range of seawater DOC concentrations (35-80 microM C and higher); with certain modifications it has proved to be both seaworthy and amenable to automated analysis; and the reliable and relatively easy to operate HTC analyzer is commercially available and easily combined with a total nitrogen analyzer for simultaneous measurements of both parameters in the same sample. In this review we summarize some aspects of sample collection, handling and the analytical chemistry of the DOC analysis by the HTC technique in marine study.